1. Field of the Invention
The present invention relates to a recording material that utilizes the photosensitivity of a diazo compound. More specifically, the invention relates to a yellow color-forming type heat-sensitive recording material that has improved color forming property and raw stock storability.
2. Description of the Related Art
Advancements in the performance of the heat-sensitive recording materials have led to a strong demand for a diazo heat-sensitive recording material prepared using a diazonium salt compound and a coupler to exhibit yellow color-forming property as well as improved raw stock storability and color density.
Recording materials that utilize the photosensitivity of the diazonium salt compound may be roughly classified into three types: a wet developing type, a dry developing type, and a thermal developing type. Among these types, the thermal developing type has an advantage in storage since this type, unlike the wet developing type or the dry developing type, obviates use of a developer.
Heat-sensitive recording materials must be able to suppress color formation in the background area during raw stock storage and a decrease in color density as much as possible. If the material is designed to sufficiently develop color and obtain high density even under low heating temperatures, color developing reaction tends to occur during raw stock storage even at room temperature, leading to a phenomenon of developing color in the background area which should remain white.
In order to solve the above problem, use of a specific anilide derivative as a coupler compound has been proposed. An example of this can be found in Japanese Patent Application Publication (JP-B) No. 54-3363, which proposes the preparation of a photosensitive material using a malonic acid anilide derivative as the coupler compound. Although this photosensitive material has improved storability, color density is unsatisfactory.
There has also been proposed for the preparation of heat-sensitive recording materials using, as the coupler compound, an anilide derivative in which a particular functional group is introduced into an oil-soluble group (e.g., Japanese Patent Application Laid-Open (JP-A) Nos. 9-160168, 9-216468 and 9-216469). Although these heat-sensitive recording materials provide constant effects in improved color density and raw stock storability in the background area, a further improvement is desired.
As described above, the current situation is that a satisfactory heat-sensitive recording material, which exhibits yellow color-forming property, suppresses color formation in the background area during raw stock storage, and has excellent color density, has yet to be obtained.